Selenium rectifier and method of its production



July 7, 1953 644,915

RECTIFIER AND METHOD 0F ITS PRODUCTION E. A. THURBER Erm..

Filed July 24. 195o /NVENTORS Patented July 7, 1953 Elmer A. fhlllr, :Murray .-Hill, and Leland A.

Wooten, Summit, N. J., assignors .toBell Telephone Laboratorjes, Incorporated, New` York, `N.'Y, ,.a eorporaltionofNew York Application -J-uly24, 1950, :SeriallNm 175,575

-1 This invention relates .generally to-methods of making asymrrietrical ,devices Vand more :particularly -to methods for ...making #selenium zrectifiers having anickel interface.

'Inorder .to reduce vthe adverse .effects :.on the electrical characteristics .'.of :selenium 4rectiflers which .would occurif .Ithe selenium .were deposited directly on a metal backing of steel or a member cf the iron group, .it .is Acustomary :to `interpose some ,other element, for .example-nickel, or `other metal selected from .the .iron group between the steel backing yand the selenium, "the nickel y:or other metals selected fffrom Ythe iron lgroup :are particularly advantageous since they generally do not form any chemical compounds with the selenium subsequently applied lthereon as the semiconductor layer vof the rectifier, :and .if :such compounds wouldbe `formed,'they occur as highly conductive vselenides .oflering very small ohmic resistances in the current'transfer direction fso that the ohmic losses may :be reducedto alow Value.

ylt has been found that the "physical v'properties of the surface of the nickel layer have a Ivery important effect on ythe electrical lcharacteristics of the `finished product. In thevprioreartythis nickel layer has been applied to the steel backing by `cladding plating or =byvelectrolytic deposition. Since a surface Vhaving-a certain degree of roughness is desirable it *has been foundfnecessary -to produce such a surface `on the nickel "by some.

means such as `retching or sand-blasting This entails an extra operation inthe manufacture of selenium rectiers.

One of the objects vof this invention is to simplify the ymethod of making selenium rectiers by formingin one step a nickel interfaeematrix having the `desirable degree of roughness.

Another object'of `theinvention is'to produce a selenium rectifier having performance and electrical characteristics superiorito those off-selenium rectiersmadebyother methods.

A Yfurther object .is .to produce 1a. selenium brectier that with a given applied voltage has a for- Ward current approximately one and a. half times as large as that of selenium rectifiers produced by other methods.

Another object is the improvement of methods of making selenium rectiers generally.

Features of the invention comprise forming a nickel interface on a metallic backing member on which the selenium is to be deposited by spraying or painting a suspension of finely divided high purity nickel particles in a nitrocellulose solution on the metallic backing mem- 7 Lciaiims. (o1. Y snr-,241)

bei and heating the coatedmember rfor .approi'imately fifteen minutes in a hydrogenqatmosphere .at a temperature between :00. .and 1000 C. to .drive ofi the temporary nitrocellulosegbinder anders-inter .the parts to the backing member.` A-

Theabove-mentioned and other objects and .features ,of :the :invention `will be LInici-te lfully g un- .dersteod yand appreciated Hem-:the toller/fine de: tailed description .lof the .method of manufacturing and thefdlfawrig `in which: g,

Iig. :1 y shows :in the .form of .e @hert the elec: .trical A.clfiaractersties .of selenium rectifiersfmade by this invention as compared with seleniur n rectiers using :a .cold rollednickelinterface, .des-v ign ted as ControllCellsNickelCled; and

, 2z `shows .the selenium `rectifier .wherein 4the metal backing element is4 designated as l element I0, the nickel layer as.-.element lil, `theselenium layfrfars element 'al-2, and thevcllnter-electrpde :as element I3. 4

'genera-1, the Amethodcom .rises the 1011er/- ing-g steps nFirst-the backing l.discs which maybe of .iron .or steel .are y.examineci ,ferrerease orc-i1 iilms which Vmay bepresent thereon.l Ihtisuch films are found it is necessary to `degrease.the discs fin .seme solution -such as Itriehleret'hylerle or .other suitable solvent. Also,V iftherev .an appreciable amount of rust on )the .discs fit may b e .-eund necessary to removexthe rust by ySome method suchasa `melding process fin a one to one htdmchloric facd'lsolutonfior exam-ple, l'fIheidisc is then ready ,for ithe application Lof the nickel matrix which ,may .the applied .eitheriby painting 0r byspraying with a prepared suspension .lcontaining :'nickel, Awhich :will be described in .more detail later. Eollowing the application .ofisthe nickelicoating byieither .paintingbr-spraying, v.the discs are sntered in a hydrogen atmosphere at temperatures `.of from-850 C. .to `1.000..C. for apnroximatelyeiifteen minutes;

,=It is :to 'he :noted :that the :degreasing discs .and the pickling :processes may bev :omittediffthe discsare .reasonably clean. iflhisifis amat? ter of some discretion and can be easily determined by visual observation after a few tests.

A typical nickel coating mixture may have the proportionate composition of 400 grams of a 325- mesh size nickel powder in 200 milliliters of a 2-per cent solution of nitrocellulose solution in amyl acetate. This is ground with riddled flint ypebbles of the order of 1/4 inch diameter for about hours at which time there is added 50 milliliters of amyl acetate and 50 milliliters of butyl cellosolve. The mixture is then rolled for approximately one hour and strained through a vof the.

The nickel coated discs are then placed in a` furnace having a hydrogen atmosphere with the furnace temperature between 805 C. and 1000 C. This heat treatment is continued for approximately fifteen minutes during which time the nickel is sintered to the iron backing disc, thus producing a matrix-like nish of desired rough ness. A selenium layer can then be applied to the nickel coating in any one of several wellknown manners such as for example evaporating iodized selenium onto the coating.

After the selenium coating has been applied to the nickel matrix, a counter electrode is applied to said selenium coating. This counter-electrode may be applied in well-known manners and can be any one of a number of materials such as antimony, thallium, tin-cadmium-thallium alloy, tin-bismuth-cadmiurn alloy, or other suitable, well-known materials.

The superior electrical characteristic of selenium rectifiers produced by the method of this invention over selenium rectifiers produced by other methods is shown in the drawing wherein a selenium disc having a cold-rolled nickel interface has been chosen for comparison. It is to be noted that from .87 volt to .98 Volt is required to pass 1000 milliamperes through a selenium rectifier made by the processes described herein whereas one volt applied across the selenium rectifier having a cold-rolled interface will only produce from 520 to 860 milliamperes.

It is to be understood that the above-described method of producing selenium rectifiers is but a preferred example of the same and that various changes can be made in materials, and heat treatment time and temperatures without departing from the scope and spirit of the invention.

What is claimed is:

1. 'I'he method of making a dry rectifier which comprises the steps of mixing nickel powder in a nitrocellulose solution, grinding said solution for approximately 100 hours, adding amyl acetate,

adding butyl cellosolve, rolling for approximately i one hour, straining through a sieve, applying the strained product to a metallic backing element, sintering said backing element at a temperature of from 850 C. to 1000 C. for approximately 15 minutes in a hydrogen atmosphere, applying a layer of selenium on the nickel coating, and applying a counter-electrode on said selenium layer.

2. The method of making a dry rectifier which liters of amyl acetate, adding 50 milliliters of butyl cellosolve, rolling the mixture for approximately one hour, then straining said mixture through a 20G-mesh sieve, applying 3 to 6 milligrams of nickel from the strained suspension to each square centimeter of a backing element, sintering said coated backing element at a temperature of from 850 C. to 1000 C. in a hydrogen atmosphere for approximately 15 minutes, applying a layer of selenium on the nickel coating, and applying a counter-electrode on said selenium layer.

3. The method of making a dry rectifier which comprises mixing nickel powder in a nitrocellulose solution, grinding said suspension with riddled flint pebbles for approximately 100 hours, adding amyl acetate, adding butyl cellosolve, rolling the comprises the mixing of 400 grams of nickel G0 powder With 200 milliliters of nitrocellulose solution, grinding said mixture with riddled flint pebbles for approximately 100 hours, adding 50 millisuspension for approximately one hour, applying from 3'to 6 milligrams of the nickel to each square centimeter of a backing element of a member of the iron group, wetting the coated backing elements with amyl acetate, sintering the dried coated backing elements in ahydrogen atmosphere at a temperature of from 850 C. to 1000 C. for about l5 minutes, evaporating in a vacuum a layer of selenium of the resultant nickel coating, and applying a counterelectrode on said selenium layer.

4. A dry rectifier comprising a base plate electrode, a coating of finely divided particles of a metal of the iron group sintei'ed to said base plate electrode, a selenium layer overlying said metal coating, and a counter-electrode on said selenium layer.

5. A dry rectifier comprising a base plate electrode, a thin matrix coating of finely divided particles sintered to said base plate, said coating consisting essentially of from 3 to 6 milligrams of nickel per square centimeter, a selenium layer overlying said coating, and a counter-electrode on said selenium layer. 6. A dry rectifier comprising a ferrous base plate electrode, a thin matrix coating of finely divided nickel particles sintered to said base plate, a selenium layer overlying said nickel coating, and a counter-electrode on said selenium layer.

'7. A dry rectifier comprising an iron base plate electrode, a uniformly thin matrix coating of finely divided nickel particles sintered to said base plate, said nickel coating consisting of from 3 to 6 milligrams of nickel per square centimeter, a selenium layer overlying said coating, and a counter-electrode on said selenium layer.

ELMER A. THURBER. LELAND A. WOOTEN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,199,104 Johnson et al Apr. 30, 1940 2,462,906 Sauerborn Mar. l, 1949 2,524,270 Pelfrey Oct. 3, 1950 

7. A DRY RECTIFIER COMPRISING AN IRON BASE PLATE ELECTRODE, A UNIFORMLY THIN MATRIX COATING OF FINELY DIVIDED NICKEL PARTICLES SINTERED TO SAID BASE PLATE, SAID NICKEL COATING CONSISTING OF FROM 3 TO 6 